[RFC PATCH v2 2/3] sched/fair: adapt scheduler group weight and capacity for parked CPUs

Tobias Huschle
2025-02-17T11:33:19Z

Parked CPUs should not be considered to be available for computation.
This implies, that they should also not contribute to the overall weight
of scheduler groups, as a large group of parked CPUs should not attempt
to process any tasks, hence, a small group of non-parked CPUs should be
considered to have a larger weight.
The same consideration holds true for the CPU capacities of such groups.
A group of parked CPUs should not be considered to have any capacity.

Signed-off-by: Tobias Huschle <huschle@linux.ibm.com>
---
kernel/sched/fair.c | 18 ++++++++++++++----
1 file changed, 14 insertions(+), 4 deletions(-)

diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index 5eb1a3113704..287c6648a41d 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -9913,6 +9913,8 @@ struct sg_lb_stats {
unsigned int sum_nr_running; /* Nr of all tasks running in the group */
unsigned int sum_h_nr_running; /* Nr of CFS tasks running in the group */
unsigned int sum_nr_parked;
+ unsigned int parked_cpus;
+ unsigned int parked_capacity;
unsigned int idle_cpus; /* Nr of idle CPUs in the group */
unsigned int group_weight;
enum group_type group_type;
@@ -10369,6 +10371,8 @@ static inline void update_sg_lb_stats(struct lb_env *env,
*sg_overutilized = 1;

sgs->sum_nr_parked += arch_cpu_parked(i) * rq->cfs.h_nr_queued;
+ sgs->parked_capacity += arch_cpu_parked(i) * capacity_of(i);
+ sgs->parked_cpus += arch_cpu_parked(i);

/*
* No need to call idle_cpu() if nr_running is not 0
@@ -10406,9 +10410,11 @@ static inline void update_sg_lb_stats(struct lb_env *env,
}
}

- sgs->group_capacity = group->sgc->capacity;
+ sgs->group_capacity = group->sgc->capacity - sgs->parked_capacity;
+ if (!sgs->group_capacity)
+ sgs->group_capacity = 1;

- sgs->group_weight = group->group_weight;
+ sgs->group_weight = group->group_weight - sgs->parked_cpus;

/* Check if dst CPU is idle and preferred to this group */
if (!local_group && env->idle && sgs->sum_h_nr_running &&
@@ -10692,6 +10698,8 @@ static inline void update_sg_wakeup_stats(struct sched_domain *sd,
sgs->sum_nr_running += nr_running;

sgs->sum_nr_parked += arch_cpu_parked(i) * rq->cfs.h_nr_queued;
+ sgs->parked_capacity += arch_cpu_parked(i) * capacity_of(i);
+ sgs->parked_cpus += arch_cpu_parked(i);

/*
* No need to call idle_cpu_without() if nr_running is not 0
@@ -10707,9 +10715,11 @@ static inline void update_sg_wakeup_stats(struct sched_domain *sd,

}

- sgs->group_capacity = group->sgc->capacity;
+ sgs->group_capacity = group->sgc->capacity - sgs->parked_capacity;
+ if (!sgs->group_capacity)
+ sgs->group_capacity = 1;

- sgs->group_weight = group->group_weight;
+ sgs->group_weight = group->group_weight - sgs->parked_cpus;

sgs->group_type = group_classify(sd->imbalance_pct, group, sgs);

--
2.34.1